UF-binders are used in a number of products. For example, they are useful as binders for nonwoven fibrous mats or abrasives applications. When used as a binder, the UF-binders may be modified with polymer latex, such as acrylic, acrylate, styrene polymers or copolymers such as styrene-butadiene, styrene maleic anhydride, and vinyl monomers such as polyvinyl acetate. Acrylic copolymer latex, such as a self-cross linking acrylic copolymer of an anionic emulsifying type has been used as one component of at least a two component binder for bonding glass fibers and particulate thermoplastic to make a glass fiber reinforced sheet that can later be hot molded into various shapes and articles.
These modifiers are added because UF-resins are very brittle upon curing, and this can cause certain strength properties to decrease due to failure mechanisms associated with brittle systems. However, the use of latex polymer in the binder, alone or as a UF-modifier, increases process time and product cost. Using polymer latex as a binder, or adding polymer latex to UF-binder, is expensive as compared to using UF-polymer solutions as binders. Also, handling of the latex solutions requires large storage facilities with associated transportation costs, handling and mixing processes that complicate binder preparation.
Moreover, the acidic nature of latexes is likely to affect the pH and reactivity, and thus the cure speed and performance, of the UF-resin. In addition, common neutralizers of latex acids can react with UF-resin to consume free formaldehyde, lower pH, and/or decrease final product shelf life.
Shelf life of UF binders as it pertains to the manufacture of wet laid nonwoven fiber mats is determined by measuring both the neat binder integrity and its water dilution stability. Neat resin integrity is depicted as supplied binder characteristics such as viscosity and uniformity. Water dilution stability is depicted as the amount of precipitation that occurs in water over time. Precipitation of binder will cause fall-out during mat processing, creating need for maintenance downtime and the addition of unnecessary costs to the process. As UF binder ages, the viscosity will increase, separations can occur, and water dilution properties will diminish, eventually making the binder unfit for use as a wet-laid nonwoven binder. Standard non-latex modified UF resin binder typically has a shelf life (neat resin integrity and dilution stability) up to about 30 days.
Latexes can maintain their “neat” shelf life for up to and often in excess of 6 months, but their water dilution properties are more sensitive. When latexes are diluted, their particles move further from one another, destabilizing the surfactant and ionic protection in water. This effect is exaggerated when mixed in UF resin because of the additional polymer and chemical interactions. Latex can significantly decrease the shelf life of a UF resin.
U.S. Pat. Nos. 4,258,098; 4,560,612 and 4,917,764 disclose the use of styrene-butadiene latex-modified, UF resin compositions as a binder for glass fiber mats.
U.S. Pat. No. 5,334,648 discloses emulsion copolymers, for use as UF resin modifiers, formed from vinyl chloride monomers, softening monomers, and functional monomers. These binders are particularly useful as glass mat binders for the production of roofing shingles.
U.S. Pat. No. 5,389,716 discloses a binder composition for fibrous mats which includes a stable mixture of an aqueous aldehyde condensation polymer-based resin and fire retardant latex. The weight ratio of the latex to the resin is at least 1:1. The composition optionally includes an amount of silica colloid sufficient to enhance the flame resistant property.
U.S. Pat. No. 5,518,586 discloses a UF resin modified with a water-insoluble anionic phosphate ester used as binder in the preparation of glass fiber mats using a hydroxyethyl cellulose white water system.
U.S. Pat. No. 5,804,254 discloses a method for flexibilizing a glass fiber nonwoven bound with a cured UF resin binder, where the binder includes a cured UF resin and 0.5-5% by weight, based on the weight of the UF resin, of a water-soluble polymer comprising 40-100% by weight, based on polymer weight, of a polymerized ethylenically unsaturated carboxylic acid monomer, the polymer having a weight average molecular weight from 100,000 to 2,000,000.
U.S. Pat. No. 5,851,933 discloses method for making non-woven fibrous mats. The mats comprise glass fiber bonded together with a dried and cured mixture of aqueous UF resin and a self crosslinking copolymer of vinyl acrylic or polyvinyl acetate.
U.S. Pat. No. 5,914,365 discloses an aqueous UF fiber mat adhesive binder formulation modified by the addition of a minor amount of a water-soluble, styrene-maleic anhydride (SMA) copolymer.
U.S. Pat. No. 6,384,116 discloses a binder composition comprising a UF resin modified with a water-soluble non-ionic amine oxide and optionally further modified with anionic acrylic latex and/or a water-soluble polymer comprising 40-100% by weight, based on polymer weight, of a polymerized ethylenically unsaturated carboxylic acid monomer. The polymer has a weight average molecular weight from 100,000 to 2,000,000.
U.S. Pat. No. 6,544,911 discloses a coated fiber mat where the coating comprises a cured, non-woven, fiber glass mat containing a polysiloxane. The fibers are fixedly distributed in a formaldehyde type binder containing a binder modifier which is a crosslinked styrene/acrylic polymer.
U.S. Pat. No. 6,642,299 discloses an aqueous binder composition containing a UF resin modified with an additive comprising (1) styrene acrylic acid or styrene acrylate, (2) an adduct of styrene, maleic anhydride, and an acrylic acid or acrylate or (3) a physical mixture of a styrene acrylic acid or styrene-acrylate copolymer and a styrene-maleic anhydride copolymer. The resulting binder is used in the preparation of fiber mats.
U.S. Pat. No. 6,682,574 discloses use of UF-resin as a binder for abrasive articles and is by incorporated herein by reference in its entirety.
In light of the above, there is a need in the art for UF resin binder compositions, which provide for improved wet and dry tensile properties, tear strength, cure speed and mat caliper. There is another need in the art for UF resin binder compositions which provide a lower raw material cost, when compared to traditionally modified binders. There is still another need in the art for UF resin binder compositions which may be supplied in a one-piece package and which exhibits adequate foam control, without excessive amounts of defoamers.